28 The Drainage of Fens and Low Lands. 



to their full extent in floods, and lowered when the flood is 

 over, so as to regulate the water in the drain to a certain 

 fixed height for the purposes of navigation, or for the supply 

 of water to the ditches for fencing or other purposes. These 

 drains being frequently used for barges, one of the openings 

 is in this case provided with lock doors for the admission of 

 craft when the doors are not open. 



Smaller sluices, w ith openings not exceeding 4 to S feet, are 

 made either with a single door, hung in the same manner as 

 already described, or with " tankard lid " doors, the door being 

 hung by a pair of double-acting hinges from the top, and fre- 

 quently provided with a counterbalance weight attached to a 

 lever fastened to the door. 



An improved method of hanging flap doors has been designed 

 by Mr. Stoney, by the use of which this description of sluice 

 doors may be used of considerable size. Attached to the flap or 

 door are a pair of lever bars, having counterbalance weights at 

 the upper end. These bars are carried on the segment of a circle, 

 the centre of which is situated in the centre of gravity of the 

 moving mass. This segment rocks on a horizontal to the path 

 situated above the water-level, making the friction less than 

 when fixed pivots are used, and rendering the opening and 

 closing very easy. Doors of this description were used for the 

 sluices of the Ballyteigne and Kilmore Reclamation Works, a 

 description and illustration being given in the * Engineer ' of 

 April 29, 1887. These doors, 6 feet 3 inches wide by 4 feet 6 

 inches high, were found to open with a head of from J to f inch. 



In addition to the sluice doors at the outlet, it is frequently 

 desirable to place doors at the end of drains discharging into 

 the main outfalls, to prevent backing up of the water in heavy 

 floods and at tide time, when the water accumulates, especially 

 where the main drain has to receive water fi-om high land. 

 By the use of these doors a large amount of embanking may 

 be saved, and even where embankments already exist the 

 erection of doors saves great pressure, and the risk of a breach, 



